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Daily News Blog

23
Sep

Study Adds to 40 Year Analysis Linking Brain Cancer to Pesticide Exposure

(Beyond Pesticides, September 23, 2021) A study by Claremont Graduate University finds exposure to agricultural pesticides increases brain cancer risk up to 20 percent. This study expands on a 1998 study evaluating brain cancer risk among the farm population using epidemiologic studies.

The etiology (cause) of brain cancer is inconclusive for many forms, including glioma and meningioma. Brain cancer risk factors include family history and exposure to radiation. However, geographical variance in brain cancer incidents suggests environmental pollutants like pesticides contribute to risk. Various research studies already note the adverse effects pesticide exposure has on the brain. These effects range from headaches and tumors to learning and developmental disabilities among children and adults. Although general cancer incidents are decreasing, brain and nervous system cancers are rising. Therefore, studies like this highlight the need to reevaluate pesticide exposure limits for those working with or around agricultural chemicals to prevent chronic, deadly diseases. The study researchers note, “This comprehensive review and meta-analysis encompassing 42 years of the epidemiologic literature and updating two previous meta-analyses by 20 years supports an association between farming and brain cancer incidence and mortality.[…]Our analyses suggest that the elevated risk has been consistent over time, and the addition of newer studies (i.e., those published since 2000) does not change this conclusion.”

Researchers conducted a literature review using PubMed and Agricola databases to assess studies evaluating the relationship between farming and brain cancer. The researchers reviewed meta-analysis studies to harmonize findings published between January 1997 and August 2019. In total, researchers evaluated 52 different studies.

The study results demonstrate that 77 percent of studies have a positive association between brain cancer and farming, with an elevated risk factor between 1.03 to 6.53 times. Therefore, the meta-risk analysis finds the brain cancer mortality/morbidity rate to be 13 percent. According to demographic information, white farmers have the highest rate of brain cancer. However, those managing livestock, where insecticides are widely used, have higher rates of brain cancer incidents than those managing crops. Overall, farmers experiencing pesticide exposure have a greater than 20 percent increased risk of brain cancer. Although there are discrepancies among studies, evidence from the previous 40 years, including the 20 years evaluated in this study, supports associations between brain cancer and chemical pesticide exposure from farming.

The nervous system is an integral part of the human body and includes the brain, spinal cord, a vast network of nerves and neurons. These components are responsible for many of our bodily functions—from the senses to movement. However, exposure to chemical toxicants, like pesticides, may cause neurotoxic effects or exacerbate preexisting chemical damage to the nervous system. The impacts of pesticides on the nervous system, including the brain, are hazardous, especially for chronically exposed individuals (e.g., farmers and farmworkers) or during critical windows of vulnerability and development (e.g., childhood, pregnancy). Mounting evidence over the past years shows that chronic exposure to sublethal (low) levels of pesticides adversely affects the central nervous system (CNS). Specifically, researchers identify agricultural chemical exposure as a cause of many adverse CNS impacts. In addition to CNS effects, pesticide exposure can impact a plethora of neurological diseases. For instance, farmworkers and their children experience higher rates of neurological diseases from exposure to carcinogenic (cancer-causing) and neurotoxic compounds readily used in conventional, chemical-intensive agriculture. These diseases include amyotrophic lateral sclerosis (ALS) and Parkinson’s diseasedementia-like diseases such as Alzheimer’s, and other effects on cognitive function. Therefore, advocates say it is essential to avoid toxic chemical exposure to lessen potential acute and chronic health risks.

Pesticide use is widespread and direct exposure from applications or indirect exposure from residues pose a threat to human health. Children are more vulnerable to the impact of pesticides as their bodies are still developing. Furthermore, a mother’s exposure to environmental toxicants while pregnant may increase the likelihood of developing brain malformations as most developmental disabilities begin before birth. A plethora of studies not only link childhood pesticide exposure, but prenatal pesticide exposure, as well, to brain tumor development. The number of children with neurodevelopmental disabilities is increasing in the U.S., and many children in rural areas—where pesticide use is most prevalent—have a higher rate of neurological disabilities. Children living on or in proximity to farms are more likely to encounter these toxic chemicals from performing farm-related activities (i.e., storing/handling pesticides, fieldwork) or leisure activities around farms (i.e., swimming in nearby contaminated water, eating crops from the field). Pesticides can have various impacts on cognitive function that are not easily classifiable with exposure-response. Headaches are the most common symptom of pesticide applications, but exposure can have confounding impacts on human health as headaches often accompany other pesticide poising symptoms. Therefore, it is essential to effectively monitor and assess pesticide exposure for the sake of human health.

The study results find an increased risk for brain cancer among those working with livestock. Many pesticides used on livestock are insecticides that specifically impact the nervous system of invertebrates. However, many studies demonstrate that exposure to pesticides, such as organophosphate insecticides, like chlorpyrifos, have endocrine disruption properties that induce neurotoxicity via acetylcholinesterase (AChE) inhibition. A 2015 Harvard University meta-analysis found that indoor use of insecticides was associated with a 47 percent increase in childhood leukemia and a 43 percent increase in childhood lymphoma. However, various herbicides, including paraquat, have links to neurotoxic impacts like Parkinson’s disease and loss of senses (i.e., hearing, smell, sight). Furthermore, a 2008 study found that women who reported using herbicides have a more than doubled risk for meningioma brain cancer compared with women who never use herbicides. The brain cancer risk increases significantly with increasing years of cumulative herbicide exposure. A majority of exposure comes from handling herbicide-contaminated produce in grocery stores/restaurants, rather than direct pesticide application.

This study adds to the growing body of research supporting a link between neurological problems and individuals with frequent exposure to pesticides. The journal Occupational and Environmental Medicine indicates that farmworkers and persons exposed to high levels of pesticides have an increased risk of developing brain tumors, especially gliomas – a tumor of the nervous system. Furthermore, this study confirms previous studies  that find farmworkers experience higher rates of specific cancers, like brain cancer. Farmworkers are at the greatest risk of pesticide-induced disease and their average life expectancy bears this out. According to the National Farm Worker Ministry, farmworkers have an average life span of 49 years, a 29 year difference from the general U.S. population. The researchers conclude “…that the synthesis of evidence from over 40 years of epidemiologic literature supports an increased risk of brain cancer from farming with its potential for exposure to chemical pesticides. Increasing organic farming practices is one means to reduce the exposure of farmers to chemical pesticides.”

Globally, cancer is one of the leading causes of death, with over eight million people succumbing to the disease every year. Notably, the International Agency for Research on Cancer (IARC) predicts an increase in new cancer cases to increase from 19.3 million to 30.2 million per year by 2040. Several studies link pesticide use and residue to various cancers, from more prevalent forms, like breast cancer, to rare forms like kidney cancer nephroblastoma (Wilms’ tumor). Therefore, studies related to pesticides and cancer will aid in future understand of the underlying mechanisms that cause the disease.

It is essential to understand the health implications of pesticide use and exposure on humans, especially if pesticides increase chronic disease risk. Beyond Pesticides tracks the most recent news and studies related to pesticides through the Daily News Blog and Pesticide-Induced Diseases Database (PIDD). This database supports the clear need for strategic action to shift away from pesticide dependency. For more information on the adverse effects of pesticides on human health, see PIDD pages on cancer (including brain cancer), brain and nervous system disordersendocrine disruption, and other diseases. Furthermore, to learn more about farmworker protection, please visit Beyond Pesticide’s Agricultural Justice page.

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

Source: Claremont Graduate University 

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